Method of treating lead-in wires of electrode tubes



United States Patent 3,261,089 METHOD OF TREATING LEAD-IN WIRES 0F ELECTRODE TUBES Heinrich .l'arczyk, Reinheim, Germany, assignor, by mesne assignments, to Robert Bosch G.m.b.H., Stuttgart, Germany No Drawing. Filed Jan. 8, 1963, Ser. No. 250,007 Claims priority, application Germany, Jan. 9, 1962,

J 7 Claims. (a. 29-527 The present invention relates to a method of treating lead-in wires of electron tubes and, more particularly,

the present invention is concerned with protecting the portions of the lead-in wires which are adjacent to the glass body through which the wire extends.

The lead-in wires of electron tubes, for instance of tubes used in communication systems, which are passing through glass bodies such as glass discs generally are contacted and attacked by a hot gas flame during the melting-through or sealing-in with the glass disc. Thereby considerable oxidation or scale formation will take place at the surface of the portions of the lead-in wire which extend from and are adjacent to the glass disc or the like through which the wire extends. The scale layer interferes with the further use of the sub-assembly consisting, e.g., of the glass disc with the wire sealed therein and extending therethrough, sinceon the one hand the soldering of a metal terminal member on the outwardly extending wire portion and-on the other hand the welding of the Wire portion extending in opposite direction to metal electrode portions which eventually will be located in the interior of the electrode tube is made diflicult by the oxidation or scale formation on the wire surface. It is also frequently required that the electric conductivity between the assembly of the lead-inwire and conductor members which are soldered or welded thereto is not impaired. It may be noted that throughout this application and the claims attached thereto the terms soldering and welding are used interchangeably.

It is possible to remove the scale layer by various mechanical or chemical means known in the art, for instance by applying strong acids, or using strong acids in connection with electrolytic processes, or by mechanical methods such as sanding or abrasive treatments, as well as by polishing the portions of the wire extending outwardly of the glass disc or the like.

After assembly of the various electrode components, these wire portions are again exposed to the gases emanating from a flame and thereby the previously chemically clean surface of the wire may be again oxidized or subjected to scaling. However, it is undesirable to have within the electrode tube oxidized wire surfaces since the oxidized portions may tend to dust formation or possess an undesired reactivity. In order to achieve the desired high conductivity of joints including these exposed lead-in wire portions and to avoid sources of ion formation within the electron tube it is therefore sometimes required to repeat the above described measures for removing scale and oxidized surface layers from the wire portion which will be located in the interior of the electron tube. It has also been proposed to apply to the exposed wire portions which will extend outwardly of the electron tube, for instance, a nickel layer in order to facilitate soldering of these portions.

However, all these steps for a second removal of scale and, for instance, electrolytically applying a nickel coating to the outwardly extending wire portions are rather involved and thus expensive and are also connected with other disadvantages and difficulties. Mechanical treatment of the leadin wire portions extending outwardly of the glass disc or the like for the purpose of removing an outward layer thereon is also usually inadvisable because during such mechanical treatment, the lead-in wire may be bent and the tightness of the wire-glass seal may be endangered.

It is therefore an object of the present invention to overcome the above discussed difficulties and disadvantages.

It is a further object of the present invention to provide a sub-assembly of lead-in wires extending outwardly through opposite faces of a glass disc or the like and forming a tight seal with the latter, which lead-in wires will not be subject to oxidation and will be capable of being soldered or welded in a reliable manner and without impairing the electric conductivity of the connection formed thereby.

It is yet another object of the present invention to achieve the above-discussed objecives in a particularly simple and economical manner.

With the above and other objects in view, the present invention contemplates a method of treating lead-inwires of electron tubes, comprising the steps of sealing a portion of a metal wire spaced from the opposite end portions thereof in a glass body, thereby exposing the portions of the wire adjacent to the sealed-in portion thereof to heat and causing scale formation on the heat exposed wire portions, removing the scale from the exposed wire portions, and forming on the now scale-free surface of the exposed wire portions, respectively, a composite metal layer consisting of an outer gold layer and an inner silver layer, the silver layer adhering to and contacting the scale-free wire surface and the outer gold layer, whereby upon subsequent exposure to heat a protective silvergold alloy layer will be formed on the surface of the exposed wire portions, respectively, preventing scale formation thereon so that a reliable soldering connection between the surface portion and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

According to the present invention, the lead-in wires will be descaled after glass beads have been formed on the same or after the lead-in wires have been sealed in a glass disc or the like with opposite end portions of the lead-in wires extending outwardly from the glass disc or other glass body. The lead-in wires preferably will consist of copper or alloys as Kovar or the like suitable for glass sealings known in the art.

The descaling of the exposed end portions of the lead-in wires which extend outwardly of the glass body to which the lead-in wires are sealed can be carried out in conventional manner in a chemical bath with or without an electrolytic process or in other ways known to those skilled in the art. Thereby, a chemically clean surface will be formed on the portions of the lead-in wire which extend outwardly from the glass body. These chemically clean exposed surface portions are then covered with a composite metal layer, namely, first with a silver layer and thereafter with a gold layer superposed upon the previously formed silver layer.

The thus treated lead-in wires are capable to endure subsequent heat treatment, for instance for the purpose of fusing the previously formed glass beads with a glass disc or the like or for sealing into the glass flask of an electron tube, without scale formation and will, after such heat treatment, possess a surface consisting of a shining silver alloy of advantageous appearance and excellent soldering qualities. The alloy of silver and gold which is formed during such heat treatment need to contain only a very small proportion of gold, for instance between 3 and 5% of gold. Such silver-gold alloys are resistant against corrosion by oxygen, moisture and many chemical corrosive substances even if the gold content of the alloy is as low as 2%.

In view thereof, it is preferred to form the outer gold layer which is superposed upon the silver layer on the exposed wire portion so that the gold layer will have weight equal to only between about 3 and 15% of the combined weight of the silver and gold layers or so that the silvergold alloy which is formed during subsequent heat treatment will have a gold content of between about 3 and 15 The practical importance of the method of the present invention is particularly apparent in the mass production of electron tubes, for instance for communication systems, since the proportion of rejects is reduced and less manual labor is required due to the fact that a second descaling, or deoxidizing of the exposed wire portions is no longer necessary.

Thus, the method of the present invention, for instance, may be carried out by sealing copper wire in a glass disc so that opposite end portions of the wire extend outwardly at opposite faces of the glass disc, cleaning the exposed opposite end portions of the wire either mechanically or chemically so that the Wire surface will be a clean metal surface of the same composition as the entire wire, for instance of copper, whereupon in succession a silver and thereafter a gold layer is applied to the cleaned exposed wire surface portions in conventional manner, for instance by electrolytic plating. Upon subsequent exposure to heat during the further processing of the glass-wire sub-assembly of the electron tube, the superposed silver and gold layers will form a protective silver-gold alloy so that no further scaling or oxidation of the thus protected exposed wire surfaces will occur, without impairing the welding and soldering properties of the wire. The thickness of the silver layer may vary between microns and 80 microns, that of the gold layer between 1 and 10 microns; with a thickness of 60 microns of silver and 6 microns of gold very satisfactory operating results have been obtained.

The essential advantages of the silver-gold alloy over a layer consisting only of gold are the following: Gold has a lower conductivity than an alloy with higher silver content and cannot be galvanized without an intermediate layer; the gold-silver alloy has a higher resistivity against mechanical stresses, the alloy is cheaper.

Other layers with similar electric and mechanic properties for forming the protective layer may be found, e.g., alloys of silver and platinum metals, but as the electroplating of platinum is more diflicult and its price is much higher, the advantages of the silver-gold alloy prevail in all practical conditions of the discharge tube manufacture.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from he standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a metal wire spaced from the opposite end portions thereof in a glass body, thereby exposing the portions of said wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; and forming on the now scale-free surface of said exposed wire portions, respectively, a composite metal layer consisting of an outer gold layer and an inner silver layer, said silver layer adhering to and contacting said scale-free wire surface and said outer gold layer, whereby upon subsequent exposure to heat a protective silver-gold alloy layer will be formed on said surface of said exposed wire portions, respectively, preventing scale formation thereon so that a If} reliable soldering connection between said surface portion and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

2. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a copper wire spaced from the opposite end portions thereof in a glass body, thereby exposing the portions of said wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; and forming on the now scale-free surface of said exposed copper wire portions, respectively, a composite metal layer consisting of an outer gold layer and an inner silver layer, said silver layer adhering to and contacting said scale-free wire surface and said outer gold layer, whereby upon subsequent exposure to heat a protective silver-gold alloy layer will be formed on said surface of said exposed copper wire portions, respectively, preventing scale formation thereon so that a reliable soldering connection between said surface portion and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

3. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a metal wire spaced from the opposite end portions thereof in a glass body, thereby exposing the portions of said wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; and plating the now scale-free surface of said exposed wire portions, respectively, with a composite metal layer consisting of an outer gold layer and an inner silver layer, said silver layer adhering to and contacting said scale-free wire surface and said outer gold layer, whereby upon subsequent exposure to heat a protective silver-gold alloy layer will be formed on said surface of said exposed wire portions, respectively, preventing scale formation thereon so that a reliable soldering connection between said surface portion and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

4. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a metal wire spaced from the opposite end portions thereof in a glass body, there by exposing the portions of said wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; and forming on the now scale-free surface of said exposed wire portions, respectively, a composite metal layer consisting of an outer gold layer and an inner silver layer, said silver layer adhering to and contacting said scale-free wire surface and said outer gold layer and the weight of said gold layer being equal to between about 3 and 15 of the combined weight of said inner silver and outer gold layers, whereby upon subsequent exposure to heat a protective silver-gold alloy layer will be formed on said surface of said exposed wire portions, respectively, preventing scale formation thereon so that a reliable soldering connection between said surface portion and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

5. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a metal wire spaced from the opposite end portions thereof in a discshaped glass body, thereby exposing the portions of said wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; and forming on the now scale-free surface of said exposed wire portions, respectively, a composite metal layer consisting of an outer gold layer and an inner silver layer, said silver layer adhering to and contacting said scale-free wire surface and said outer gold layer, whereby upon subsequent exposure to heat a protective silver-gold alloy layer Will be formed on said surface of said exposed wire portions, respectively, preventing scale formation thereon so that a reliable soldering connection between said surface portion and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

6. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a metal wire spaced from the opposite end portions thereof in a glass body, thereby exposing the portions of said Wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; and forming on the now scale-free surface of said exposed wire portions, respectively, a protective layer of a silver-gold alloy thereby preventing scale formation on the surface of said exposed wire portions so that a reliable soldering connection between said surface portions and another metal body may be formed without impairing the electric conductivity of the thus-formed connection.

7. Method of treating lead-in wires of electron tubes, comprising the steps of sealing a portion of a metal Wire spaced from the opposite end portions thereof in a glass body, thereby exposing the portions of said wire adjacent to the sealed-in portion thereof to heat and causing scale formation on said heat exposed wire portions; removing the scale from said exposed wire portions; forming on the now scale-free surface of said exposed wire portions, respectively, a composite metal layer consisting of an outer gold layer and an inner silver layer, said silver layer adhering to and contacting said scale-free wire surface and said outer gold layer; and heating said composite metal layer so as to form thereof a silver-gold alloy protecting said surface of said exposed wire portions, respectively, and preventing scale formation thereon so that a reliable fussed connection between said surface portion and another metal body may be formed Without impairing the electric conductivity of the thus-formed connection.

References Cited by the Examiner UNITED STATES PATENTS 2,941,279 6/1960 Freedman 29-4729 X 3,028,663 4/1962 Iwersen et a1. 3,207,838 9/1965 McCormack 29-492 X JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner. 

1. METHOD OF TREATING LEAD-IN WIRES OF ELECTRON TUBES, COMPRISING THE STEPS OF SEALING A PORTION OF A METAL WIRE SPACED FROM THE OPPOSITE END PORTIONS THEREOF IN A GLASS BODY, THEREBY EXPOSING THE PORTIONS OF SAID WIRE ADJACENT TO THE SEALED-IN PORTION THEREOF TO HEAT AND CAUSING SCALE FORMATION ON SAID HEAT EXPOSED WIRE PORTIONS; AND FORMING ON THE SCALE FROM SAID EXPOSED WIRE PORTIONS; AND FORMING ON THE NOW SCALE-FREE SURFACE OF SAID EXPOSED WIRE PORTIONS, RESPECTIVELY, A COMPOSITE METAL LAYER CONSISTING OF AN OUTER GOLD LAYER AND AN INNER SILVER LAYER, SAID SILVER LAYER ADHERING TO AND CONTACTING SAID SCALE-FREE WIRE SURFACE AND SAID OUTER GOLD LAYER, WHEREBY UPON SUBSEQENT EXPOSURE TO HEAT A PROTECTIVE SILVER-GOLD ALLOY LAYER WILL BE FORMED ON SAID SURFACE OF SAID EXPOSED WIRE PORTIONS, RESPECTIVELY, PREVENTING SCALE FORMATION THEREON SO THAT A RELIABLE SOLDERING CONNECTING BETWEEN SAID SURFACE PORTION AND ANOTHER METAL BODY MAY BE FORMED WITHOUT IMPAIRING THE ELECTRIC CONDUCTIVITY OF THE THUS-FORMED CONNECTION. 